This invention relates generally to electrographic apparatus and more particularly this invention relates to electrographic apparatus which produces copies of at least first and second dimensions.
Many techniques have been proposed for producing copies in which a plurality of images are produced on a single sheet. In one such technique, color separation images of an original are superimposed upon a sheet to produce a color copy of the original. An electrographic apparatus for producing colored copies is described and illustrated in commonly assigned U.S. Pat. No. 4,251,154, issued Feb. 17, 1981, for "Electrophotographic Color Copier," by M. J. Russel. The described apparatus includes a movable image transfer member for receiving related transferable color separation images in non-overlapping image areas. The image transfer member is moved along a transport path and a transfer mechanism is mounted adjacent to the transport path for transferring at spaced locations along the path the color separation images to a receiver sheet. The transfer mechanism successively positions the receiver sheet at the spaced locations in register with and in image transfer relation to the color separation images on the moving transfer member to superimpose the color separation images in register on the receiver sheet. Although the disclosed apparatus may be suitable for the purposes for which it was intended, the apparatus is limited to producing copies of a single dimension as measured in the direction of movement of the image transfer member. A receiver sheet is removed from the image transfer member and positioned in contact with the transfer member in registration with a successive image on the transfer member by means of a fixed dimension register roller which has a circumference equal to the dimension of one image area in the direction of travel of the image transfer member plus the distance between adjacent areas. Thus, for example, if letter size copies (81/2.times.11 inches) and legal size copies (81/2.times.14 inches) are produced, the circumference of the register roller is equal to 81/2 inches plus an interframe distance of approximately 11/2 inches or a total of 10 inches.
If it is desired to produce copies of greater dimension, for example, 11.times.17 copies, then both the circumference of the register rollers and the image area on the image transfer member would have to be increased in size. However, if it were desirable to produce both 81/2.times.11 and 11.times.17 inch copies with the larger sized apparatus, then certain inefficiencies in operation of such an apparatus would result. Thus, if such an apparatus were switched from producing larger copies to smaller copies, the register roller must be accelerated to reposition the copy sheet in time for the 81/2.times.11 image. This change in roller velocity results in increased power requirements for the registration roller drive, in registration inaccuracies, and in mechanical difficulties such as vibration. Alternatively, if the register roller is not accelerated, an 81/2.times.11 image produced after an 11.times.17 image must be delayed on the image transfer member, thus creating an unusually large interframe distance. This results in decreased productivity since the maximum productivity would be limited to the number of large frames imaged per hour.
Thus, it would be desirable to provide an electrographic apparatus which not only produces multiple images on a single copy but also which efficiently produces copies of different dimensions.